Yep, not that many top-tier talent in the US willing to be in the factory for the graveyard shift under high pressure. The lines run 24/7 and if anything is slightly wrong techs need to be already on site to go fix it, because it's crap tons of money for every second of downtime. That leads to a corporate culture where even R&D has similar pressures from your boss (because essentially you're always racing with the competing fabs).